From the other site:
"it appears the standard 024 crankcase flywheel side is stamped 9 1121 021 0700 and the 024S and 026 case half is stamped 9 1121 021 0701."
Or, just pull the cylinder and measure. It's going to have to come apart, eventually.
You could try sending the SN into the Stihl customer service...but, I bet they will come back with "Too old for our records."
Roy